1. Field of the Invention
The present invention relates to a continuously variable transmission including a belt type variable speed-change mechanism capable of continuously changing a speed of a rotational power from a driving power source, an endless member type power-transmitting mechanism that transmits the rotational power from the driving power source at a constant speed, and a planetary gear mechanism that combines a variable-speed rotational power transmitted from the belt type variable speed-change mechanism and a constant-speed rotational power transmitted from the endless member type power-transmitting mechanism and then output the combined rotational power, and a working vehicle including the continuously variable transmission.
2. Related Art
There have been previously proposed a continuously variable transmission (see, for example, Japanese unexamined patent application publication No. S62-028554 and U.S. Pat. No. 5,041,067, which are hereinafter referred to as prior art documents 1 and 2, respectively) that includes a belt type variable speed-change mechanism, an endless member type power-transmitting mechanism and a planetary gear mechanism, wherein a variable-speed rotational power, which is transmitted through the belt type variable speed-change mechanism from a driving power source, is input into a first element of the planetary gear mechanism, a constant-speed rotational power, which is transmitted through the endless member type power-transmitting mechanism from the driving power source, is input into a second element of the planetary gear mechanism, and a combined rotational power is output from a third element of the planetary gear mechanism.
This type continuously variable transmission is useful in that continuously variable-speed rotational power in both normal and reverse directions can be output from the third element by operating the belt type variable speed-change mechanism.
However, there is room for improvement in the conventional continuously variable transmission in view of miniaturization and formation of an overall power transmitting path.
The conventional continuously variable transmission disclosed in the prior art documents 1 and 2 is configured so that the continuously variable-speed rotational power is transmitted from a driving shaft operatively connected to the driving power source to a variable-speed driven shaft disposed parallel to the driving shaft through the belt type variable speed-change mechanism, while the constant-speed rotational power is transmitted from the driving shaft to a constant-speed driven shaft that is disposed parallel to the driving shaft and that is separate from the variable-speed driven shaft through the endless member type power-transmitting mechanism.
In the configuration, the planetary gear mechanism is supported by the constant-speed driven shaft.
More specifically, the first element is supported on the constant-speed driven shaft in a relatively rotatable manner with respect thereto in a state where the first element is operatively connected to a variable-speed gear supported by the variable-speed driven shaft in a relatively non-rotatable manner with respect thereto, the second element is supported by the constant-speed driven shaft in a relatively non-rotatable manner, and the third element is supported by the constant-speed driven shaft in a relatively rotatable manner with respect thereto.
In the thus configured conventional continuously variable transmission, the rotational power to be transmitted to the first element is first transmitted from the driving shaft to the variable-speed driven shaft that is separate from the constant-speed driven shaft, and is then transmitted to the first element through the variable-speed gear, while the rotational power to be transmitted to the second element is transmitted from the driving shaft through the constant-speed driven shaft.
That is, in the conventional continuously variable transmission, a variable-speed power transmitting path and a constant-speed power transmitting path are totally separate from each other, resulting in a problem of enlargement of the overall power transmitting path and a problem of deterioration of workability in forming the power transmitting path.